1. Field of Invention
The present invention pertains to tufted fabrics useful in the manufacture of articles such as, for example, carpets, rugs, and upholstery. More specifically, the present invention is directed to a process for manufacturing tufted fabrics, especially recyclable fabrics, which comprise a primary backing having tufts mounted therein.
2. Description of Related Art
An overview of the present technological developments with respect to the application of thermoplastic polymer adhesives to textile substrates is disclosed, for instance, in Textile World, Chemical Treatment & Finishing, February 1994, page 87 to 89. This article discloses that the increasing demand to operate at higher production rates has resulted in changes to the method by which tufted fabrics are manufactured. More specifically, these changes are characterized by the replacement of solvent-born adhesives with thermoplastic polymer (hot-melt) adhesives.
Processes employing solvent-born adhesives are considered disadvantageous inasmuch as they require large drying ovens and involve extended drying times, thereby lowering production rates. By contrast, hot-melt adhesives have a relatively short setting time and hence allow for higher production rates.
The hot-melt process is characterized by the mounting of tufts in a primary backing, followed by the application of a hot-melt adhesive to the backside of the primary backing so as to form the tufted fabric. Although the use of hot-melt adhesives allow for higher production rates, it has been noted that hot-melt adhesives also exhibit several disadvantages. For example, hot-melt adhesives can only be applied to textile fabrics at high temperatures, well above the melting temperature of the adhesive polymer. Because tufted fabric materials are often unstable at such high temperatures, the exposure of a textile fabric to the temperatures associated with the hot-melt process can result in considerable thermal shrinkage to the textile fabric. The mechanical properties of the fabric can thereby be permanently damaged. Accordingly, the hot-melt adhesive method is considered impractical or even unacceptable for several fabrics. In particular, textile fabrics formed from materials having a melting or softening temperature close to the temperature at which the hot-melt adhesive is applied cannot be effectively produced by the hot-melt adhesive method.
A further disadvantage of hot-melt adhesives is that many polymers that are otherwise suitable as adhesives are chemically unstable, sensitive to oxidation, or very hygroscopic at temperatures above their melting temperature. Accordingly, such adhesive polymers can only be applied by employing expensive closed methods such as die extrusion, in which a film of adhesive polymer is extruded and applied to the backside of a textile fabric.
In addition, hot-melt adhesives often have an undesirably high viscosity, thereby producing poor wetting properties. High wetting results in poor bonding between tufts and the primary backing and poor mutual bonding between the fibers in the tufts. The resulting tufted fabrics are sensitive to abrasive forces and have an undesirably low life-span. Consequently, these adhesives are considered unsuitable for many production processes.
The aforementioned disadvantages associated with hot-melt adhesives are especially problematic in the manufacture of tufted fabrics having an adhesive polymer formed from substantially the same polymer as the tufts and/or the backing. Such tufted fabrics are of great interest because of their attractiveness for recycling purposes.
For example, EP-A 0,508,287 discloses a recyclable tufted carpet in which the tufts and the primary backing consist of polyamide 6. The tufts are bonded to the primary backing by applying a polyamide 6 in the form of a film or powder, heated above the melting temperature, to the backside of the tufted fabric. Because the tufts are formed from substantially the same polymer as the adhesive polymer, the melting temperatures of the tufts and adhesive polymer are substantially similar. Thus, a serious risk arises of melting the tufts and the primary backing, thereby adversely affecting the mechanical properties of the tufted fabric.
The particular polyamide film and powder disclosed in the above-cited reference respectively present additional problems. For example, the polymer powder, which must have a small particle size, is very expensive. The polyamide film is applied to the tufted fabric in such a manner that excess film is present in interstitial spaces between the tufts, thereby increasing the weight of the tuft fabric without significantly contributing to the binding of the tufts. Further, the flexibility and the dimensional stability of the tufted fabric is poor. As defined herein, "dimensional stability" refers hereinafter to the extent to which dimensional changes (e.g., shrinkage) occur upon exposure to changing ambient conditions (e.g., air relative humidity and temperature).
EP-A 0,508,287 further suggests applying a copolyamide (as opposed to a polyamide) thermoplastic polymer adhesive to decrease the melting temperature of the adhesive, thereby avoiding such problems as thermal degradation and shrinkage. However, application of a copolymer is disadvantageous inasmuch as copolymers contain a substantial amount of different (co)monomers. For example, about 30 to 40% of the copolyamide must be represented by a different (co)monomer in order to depress the melting temperature of polyamide 6 about 40.degree. C. Including such large amounts of a different (co)monomer also contradicts the primary objective in the field of recyclable tufted fabrics--i.e., an increase in yield of monomer recoverable upon recycling. Moreover, copolyamides have a relatively high viscosity and hence poor wetting properties.